Euro metric and P-metric tires in the same size (i.e. Not quite as uniform as creating sizes using a formula, but they got the job done. However, since Euro metric sizes have been added over time based on the load and dimensional requirements of new vehicles, the tire manufacturers designed many new tire sizes and load capacities around the needs of new vehicles. Using metric dimensions to reflect a tire's width actually began in Europe in the late 60s. Metric or Euro metric sized tires are the ones without the "P" at the beginning, (such as 215/65R16). Since all P-metric sizes are all based on the formula for load, vehicle manufacturers can design their new vehicles (weights and wheelwell dimensions) around either existing or new tire sizes. Their load capacity is based on an engineering formula which takes into account their physical size (the volume of space for air inside the tire) and the amount of air pressure (how tightly the air molecules are compressed). P-metric sizes were introduced in the United States in the mid 70s and are installed on vehicles primarily used to carry passengers including cars, station wagons, sport utility vehicles and even light duty pickup trucks. P-metric sized tires are those with the "P" at the beginning of the tire size (such as P215/65R16). This older system is still widely used, mostly on commercial vehicles. (Load Index and Speed Rate) (Single/Duals) Often these tires are referred to as European C-Type sizes. This size system mirrors the European Metric system for passenger tires and is intended for commercial light truck vehicles sometimes referred to as “Euro Vans”. The combination of lower aspect ratios and high flotation yielded better traction on sand and soft soil found in off-road situations. Light truck high flotation tires have evolved as lower aspect ratio tires became more popular on light trucks. This sizing system mirrors the P-Metric system for passenger tires. There are three primary light truck tire sizing systems: Light Truck Metric, Light Truck High Floatation and Light Truck Numeric. Light truck tires have evolved along with the expanded applications of trucks and vans that have grown to be multi-purpose vehicles that we use for work, for recreation or as passenger vehicles. Sizing for light truck tires takes the performance requirements of the vehicle, and the tires, into account. S = Service Description (Load Index and Speed Rating) Aspect ratio appears in the size designation in most cases where it is other than 82.ħ8S = Service Description (Load Index and Speed Rating) See examples below.ĩ5S = Service Description (Load Index and Speed Rating)Įssentially,this system was a conversion of the Numeric system from inches to millimeters. It provides a better description of the tire size. The P-Metric sizing system was developed to better align with the European tire sizing system. The following are examples that identify the three sizing systems that are commonly seen today. It was developed when all tires had the same aspect ratio, and it provided only the nominal cross section width of the tire and the rim diameter in inches. Each of these systems evolved from the first tire sizing system-the Numeric Sizing system-that is now obsolete. Passenger Tire Sizing Three primary sizing systems exist for passenger tires today: P-Metric, European Metric and Millimetric. It will also provide you with information when mounting and servicing the tire. Being able to read sidewall markings will help you better understand the performance of each tire. The side of a tire contains information needed for your safety and that of your customer.
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